Polarization has become a commonplace functional requirement for reducing uncomfortable glare in eyewear lenses. Spectral filtering using dyes and dichroic coatings is also commonplace for reducing luminance and shifting hue, each with performance limitations.
It has been attempted previously to enhance vision with eyewear that includes a polarization interference filter, as exemplified in U.S. Pat. No. 7,106,509. From a practical standpoint, the filters disclosed therein are overly complex with multiple layers of retardation that create multiple output impulses from a polarized input pulse. The necessity of the many impulses is to filter in the spectral cyan, the spectral yellow, or both, while efficiently transmitting other wavelengths. Such an eyewear filter with acceptable angular color uniformity would require a minimum of six to ten retarder films using available uniaxial materials. For the seven-layer example given therein, the retarder stack would require a minimum of 21 layers, which would be impractical for an eyewear product.
What is needed, therefore, are improved techniques for spectral filtering in eyewear lenses.